Perihelion

Earth is huddling close to the Sun for the next couple of days — it’s closest for the whole year, in fact. It’s at a point in its orbit called perihelion, and it happens every January.

There are a couple of ways to measure the separation between Earth and the Sun. There’s the way astronomers measure it, which is from the center of Earth to the center of the Sun — 91.4 million miles at perihelion. Or you can measure it from the surfaces of the two bodies, which puts the Sun almost half a million miles closer.

The distance between Earth and the Sun changes because Earth’s orbit is an ellipse — like a slightly flattened circle. Over the course of an orbit, the distance varies by about three million miles.

When the Sun is closest, as it is now, we receive about seven percent more total solar energy than when it’s farthest, in early July. But that has nothing to do with the seasons. They’re controlled by Earth’s tilt on its axis. Right now, the north pole is tilted away from the Sun, so it’s winter in the northern hemisphere, and summer in the southern hemisphere.

The changing distance does have one important impact on the seasons. When Earth is close to the Sun, it moves faster in its orbit than when it’s farther away. So that makes the length of the seasons uneven. Here in the northern hemisphere, winter is only about 89 days long, compared to 93 days of summer — extra sunlight thanks to our lopsided path around the Sun.
 

Script by Damond Benningfield